Since Ubuntu 11.10 use a new kernel, it's very difficult to have a decent support for virtualization.

VirtualBox doesn't support guest additions for ubuntu 11.10, so I can't copy to and from my ubuntu desktop and windows, which I absolutely require, plus FreeBSD seems not to be able to use DHCP without guest additions.

Virt-manager instead gives an error on launch:

Unable to open a connection to the libvirt management daemon.
Libvirt URI is: qemu:///system
Verify that:
- The 'libvirt-bin' package is installed
- The 'libvirtd' daemon has been started
- You are member of the 'libvirtd' group
unable to connect to '/var/run/libvirt/libvirt-sock', libvirtd may need to be started: Permission denied
Traceback (most recent call last):
File "/usr/share/virt-manager/virtManager/connection.py", line 1146, in _open_thread
self.vmm = self._try_open()
File "/usr/share/virt-manager/virtManager/connection.py", line 1130, in _try_open
flags)
File "/usr/lib/python2.7/dist-packages/libvirt.py", line 102, in openAuth
if ret is None:raise libvirtError('virConnectOpenAuth() failed')
libvirtError: unable to connect to '/var/run/libvirt/libvirt-sock', libvirtd may need to be started: Permission denied

The problem is solved by running virt-manager as root, but I don't like that. How do I change permissions to run Virt-Manager as user?

Actually the guest addition does work.. almost work. Everything works after installing the sh file in the Virtualbox guest addition iso. Everything except what you are mentioning. Let me get back to you when I find a solution to this. Did not know this case.
–
Luis Alvarado♦Nov 22 '11 at 17:43

Run the Linux Guest Addition installer in the Guest Ubuntu. Open the terminal, cd yourself to the mounted image (In my case is cd /media/cyrex/VBOXADDITIONS_4.1.6_74713). In your case you need to input cd /media/USER/VBOXADDITIONS_VIRTUALBOX_VERSION where USER is your username and VIRTUALBOX_VERSION is the current version you are installing. After that run the Guest Addition:

sudo ./VBoxLinuxAdditions.run (It is in the root directory of the ISO image)

Since you installed the needed packages in step 2, you should be fine after installing the Linux Addition since it will configure with no problems. Say yes to a question or two it might ask but this will not do you harm since it will be checking to see if you have the guest addition installed already. Reboot after finishing the install.

Now when the guest starts again you should see that you have several new options available like input devices, views, etc.. but the one you are needing is SHARE FOLDERS!!. To share a folder you already know that is done from the Virtualbox Menu.

But what we need is to connect to this Shared folder from the Host. To do this first create a folder in the guest which will link to the shared folder from the host. For example lets create in the guest home folder the directory virtual. Now assuming the shared host folder is also called virtual we would set this up in the guest like this:

sudo mount -t vboxsf virtual ~/virtual

Now you can access the shared folder.

NOTES ON HOW TO SHARE, AUTO MOUNT AND 3D

The name of the shared host folder must be the same as the guest folder. In the example mentioned above you have both named virtual, but it could be both named bck, shared, virtualbox, etc... This will solve several "protocol" errors.

Since mounted shares have by default root as owner, to mount them as YOU, you can do for example:

To automount a share folder add it to /etc/fstab. This way when you load the guest it will have the shared folder already mounted.

If (JUST IF!!) you by change have a editing/saving problem directly in the shared folder. Just copy over the file to another place. Edit the file, save it, copy over back to the shared folder, replacing the one in there.

If the 3D Acceleration support was not enabled when you did the virtualbox setup. Do not worry just run the guest addition again after activating it as seen here:

You can also do the Guest Addition setup from the Proprietary Driver Manager. That is, jockey-gtk As seen in this picture (This is the same as Step 2)

After all of this you should have a Virtualbox that shares folders with the host and back and has 3D acceleration. Here is an image of the outcome:

Windows Guest with Ubuntu Host

If you are using Windows Vista and up, by simply installing the Guest Addition, Sharing the folder (The same procedure as in the Ubuntu example) and rebooting the Windows Guest session you will automatically see the Shared folder between both systems.